The present invention is directed to a method of manufacturing a semiconductor device including a capacitor formed on a recrystallized polysilicon layer.
Modern electronic equipment, such as televisions, telephones, radios and computers, is generally constructed of solid state devices. Solid state devices are preferred in electronic equipment because they are extremely small and relatively inexpensive. Additionally, solid state devices are very reliable because they have no moving parts, but are based on the movement of charge carriers.
Solid state devices may be transistors, capacitors, resistors and other semiconductor devices. Typically, such devices are fabricated on a substrate and interconnected to form memory arrays, logic structures, timers and other integrated circuits. One type of memory array is a dynamic random access memory (DRAM) in which memory cells retain information only temporarily and are refreshed at periodic intervals. Despite this limitation, DRAMs are widely used because they provide low cost per bit of memory, high device density and feasibility of use.
In a DRAM, each memory cell typically includes an access transistor coupled to a storage capacitor. In order to fabricate high density DRAMs, the storage capacitors must take up less planar area in the memory cells. As storage capacitors are scaled down in dimensions, a sufficiently high storage capacity must be maintained. Efforts to maintain storage capacity have concentrated on building three-dimensional capacitor structures that increase the capacitor surface area. The increased surface area provides for increased storage capacity. Three-dimensional capacitor structures typically include trench capacitors and stacked capacitors. While trench capacitors are still used, many of the capacitors currently used are of the stacked capacitor type.
Stacked capacitors typically include first and second conductive electrodes separated by an insulator material. Often the first, or lower electrode, comprises a material such as cobalt silicide, the insulator material comprises a material such as silicon dioxide, and the second, or upper electrode, comprises a material such as titanium nitride. This is particularly the case when striving for high performance capacitors.
While the above-discussed capacitors are used as high performance capacitors, their use is not without certain drawbacks. One such drawback stems from the difficulty in forming substantially planar first, or lower electrodes. Specifically, the first, or lower electrodes, presently have varying and unpredictable amounts of roughness. This unfortunately causes the capacitors to have varying and unpredictable amounts of capacitance, as a result of the increased or decreased surface area of the first, or lower electrode. It has been observed that the varying and unpredictable amounts of roughness are particularly evident when the first, or lower electrode, is formed over a polysilicon substrate. Unfortunately, these capacitors are often formed directly on the polysilicon gate of the underlying transistor, which exaggerates this problem.
Accordingly, what is needed in the art is a capacitor that does not experience the lower electrode roughness experienced by the prior art capacitors.